This invention relates to a novel suspension media for hematological compositions, having particular utility with a red blood cell component, for devices using electronic and optical means for blood determinations, and processes for using the suspension media.
It is evident that a hematology control product must accurately indicate, on a comparative basis, what a test sample of fresh blood constitutes with regard to the determinations in question. It is further evident how important it is for the control product to simulate fresh blood, since blood components, such as red blood cells, can hemolyze slowly and undergo changes in size and shape within hours after removal from a blood donor. Similarly, white blood cells suffer degenerative changes.
Suspending medium formulations are designed for the purpose of stabilizing the attributes of the cells and/or particles suspended in them, and to have antimicrobial properties sufficient to inhibit the growth of possible contaminating microorganisms. The specific parameters of the red and white blood cells that are desirable to be measured dictate some of the necessary characteristics of a suitable suspension media for a hematology control product. It is desirable to know the volume of the red cell. Once this measurement is ascertained and the red cells have been counted, the packed cell volume or hematocrit can be computed. Therefore, the suspension media of the control product should be capable of equilibrating and stabilizing the volume of red blood cells in the sample so that its mean corpuscular volume (MCV) and red blood cell distribution width (RDW) can be measured.
Because of the sensitivity of the components of a hematology control product, such as the red blood cell component, white blood cell component, and platelet component, to the chemical compounds contained in a suspension media, it has been difficult to find a combination of chemical compounds that do not degrade or undesirably alter the characteristics of the blood cell components to be analyzed, especially over varied storage times. Frequently, a chemical compound is added to maintain the stability of a blood cell component or a certain functional property, but which might detrimentally affect one or more physical parameters of the blood cells or other blood cell determinations.
One disadvantage of prior art suspension media of hematology control products is that when used in conjunction with a red blood cell component, the control product has a short closed vial storage life. After the control product storage life, the control product does not simulate one or more of the specific parameters of the blood cells that are desirable to be measured.
Historically the effectiveness of an individual suspending media formulation has been measured by the amount of stabilization (amount of change) observed for those specific attributes of cells and/or particles that are known to change or exhibit defined trends. It is well known that mammalian red blood cells (RBC""s) used in the formulation of xe2x80x9cwhole bloodxe2x80x9d hematology controls exhibit changes in their MCV and RDW over time. It is important for the red blood cell component in the hematology control product to maintain an MCV within a defined range over a sufficient period of time in order to adequately assist in the calibration, operation, and accumulation of quality assurance data for a multi-parameter automated hematology instrument. Typically, manufacture specifications provide for a deviation of less than 6 femtoliter, and preferably less than 4 femtoliter, change from the highest MCV value to the lowest MCV value during the product""s useful life. Changes greater than 6 femtoliter do not provide the necessary utility for the hematology control product. Concomitantly, the RDW should remain consistent over a sufficient period of time to provide the necessary utility for the hematology control product.
One general approach has been used to confer some degree of stability, that is to reduce the amount of MCV change, exhibited by the RBC""s utilized in xe2x80x9cwhole bloodxe2x80x9d control. This general approach was shown by Hunt U.S. Pat. No. 3,873,467 (1975) and Wong et al U.S. Pat. No. 4,777,139 (1988) and U.S. Pat. No. 4,698,312 (1987), who used small amount of various aqueous aldehydes to stabilize the shape and size of suspended RBC""s. However, one of the disadvantages of the stabilized RBC preparations described by Wong et alxe2x80x94U.S. Pat. No. 4,777,139 (1988) is that the stabilization period required before the exhibited MCV changes become minimal is dependent on the initial level or size of the treated preparation. Equilibrations took approximately 35, 25, and 10 days for Levels I, II, and III respectively. Once, however the MCV valued stopped changing, they remained constant (within tolerances of 1 MCV unit) for 90 days or longer. However, these unequal equilibration times increase the logistical difficulty in implementing these teachings in a manufacturing setting.
Another disadvantage of the prior art media is that, when used in conjunction with red blood cells and fixed human white blood cells or white blood cell analogs that have been stored in a closed vial for an extended period of time, the control product does not accurately indicate, on a comparative basis, what a test sample of fresh blood constitutes with regard to the determinations in question.
Not withstanding the prior art suspension media, there still exists a need for new suspension media for use in a hematology control product such that a stored closed vial of the hematology control product indicates upon analysis, on a comparative basis, what a test sample of fresh blood constitutes with regard to the determinations of MCV and RDW. The increased shelf life avoids the problems associated with manufacturing logistics and customer dissatisfaction of obtaining products with a shortened time in which the products can be used.
The present invention relates to a hematology control product comprising a closed vial of a lyseable red blood cell component and a xanthine compound in an isotonic suspension medium. The xanthine compound is in an amount sufficient to provide extended shelf life of the hematology control product and the lyseable red blood cell component is present in an amount sufficient to be measurable with an automated hematology instrument. The hematology control product has a reported MCV which corresponds substantially with the MCV of human whole blood. The hematology control product has an osmolality from about 200 to 400 milliosmoles. Preferably, the xanthine compound is present in an amount from about 0.1 to 1.0% by weight/volume. More preferably, the xanthine compound comprises caffeine.
The hematology control product can further contain compatible preservative compositions in an amount sufficient to provide fungicidal and bactericidal activity. In addition, the hematology control product can contain one or more pH adjusting agents to provide a pH in the range from approximately 5.8 to 6.8.
In a further embodiment, the hematology control product further contains a white blood cell component. Preferably, the white blood cell component simulates at least three subpopulations of white blood cells.
In still a further embodiment, the hematology control product contains a white blood cell component which simulates at least four subpopulations of leukocytes.
The present invention also relates to a method of using the above described hematology control product to determine the accuracy and reproducibility of the operation of a hematology instrument comprising the steps of:
a) providing the hematology control product comprising a lyseable red blood cell component and a xanthine compound in an isotonic suspension medium, wherein the xanthine compound is in an amount sufficient to provide extended shelf life of the hematology control product and wherein the lyseable red blood cell component is present in an amount sufficient to be measurable with an automated hematology instrument and wherein the hematology control product has an reported MCV which corresponds substantially with the MCV of human whole blood, and wherein the hematology control product has a known reference value for each component type present in the product;
b) determining the reference value for each component type in the hematology control product with an automated hematology instrument; and
c) comparing the reference value for each component type obtained from step b) above with the known reference value for each component type from step a) above.
In a preferred embodiment, the method uses a mean cell volume value of the blood cell as the reference value. In addition, or in the alternative, the method can use a red blood cell distribution width value of the blood cell as the reference value.